This is amazing. I have never been so close.
For more than 50 years, Japan has been at the forefront of big physics,
creating experiments of such size and ambition that they need to be seen to be believed.
My name is Davide Castelvecchi, and I'm one of Nature's physics reporters.
In this series, I will be travelling to Japan to visit three of its flagship experiments,
delving inside Japan's big physics.
About 50 kilometres north-east of Tokyo is the city of Tsukuba,
home to Japan's largest particle physics lab – KEK.
When you arrive at KEK, you're given a radiation dosimeter to wear.
The experiments all around the facility are smashing particles together, which releases some radiation.
Although they are highly controlled and very safe, it is always good to take precautions.
I am here to see an experiment called Belle II.
My name is Mikihiko Nakao.
Half of my time, I'm working on the data acquisition system of the Belle II detector,
and half of my time, I'm working on the physics analysis.
Belle II is the second in a series of experiments built to study an often overlooked branch of particle physics –
B physics.
The 'B' in B physics refers to one of the constituent parts of a particle called a B meson.
'B' stands for 'bottom' or 'beauty'.
And these particles have some interesting properties.
B mesons are unstable particles, which are very rare in nature,
but they can be made in particle accelerators, and that is what Belle II does.
Electrons and their antimatter counterpart, positrons, collide at the centre of Belle II
and annihilate each other, producing two B mesons.
These unstable mesons immediately decay into lighter particles and fly away.
By measuring these decays and the trajectories of the particles,
researchers can look for places where the numbers don't add up,
and that may be the key to explaining some of the big mysteries in the Universe.
In particle physics, we have accumulated a lot of data,
and we have established the so-called Standard Model of particle physics,
but this is still lacking a lot of things to answer the mysteries of the Universe.
Physicists like Mikihiko believe that there could be some new physics to discover
which can explain some of these mysteries.
One example is that no antimatter is observed in our Universe,
and we don't know how this antimatter-matter imbalance was generated at the very beginning.
Something tipped the balance, some difference in behaviour between particles and antiparticles.
This difference is called CP violation, and it is one of the things Belle II is studying using B mesons.
Back in 2001, Belle – the predecessor to Belle II – was among the facilities
that first measured the CP violation in the decay of a B meson,
and Belle II is looking to confirm if those were hints of new physics or just statistical flukes.
Mikihiko took me on a tour of the detector to get a look at the engineering that makes this all possible.
So, now we are coming to the gallery area of the Belle II experimental hall,
and usually, we cannot go around the detector area but because we are now in a shutdown time,
we are allowed to go there.
The hole containing Belle II is vast,
and around the gallery are flags from every country that has collaborated on the experiment over the years,
from Saudi Arabia to Vietnam.
When I visited, the detector was still not fully operational.
It had run some short tests, but it had been shut down again.
So, now we are on top of the beam line, and you can actually see the two beam pipes.
Huge metal yokes had been pulled apart and the detector had been almost totally deconstructed,
which gave us a rare chance to look inside.
Off to one side in a clean space, researchers were testing the most advanced part of Belle II –
the silicon vertex detector.
So, this is the detector which can measure the origin of the particle
up to a resolution of less than 100 micrometres, and this will go into the centre of the detector.
And it is by measuring these particles with incredible levels of detail
that Mikihiko hopes to discover new physics.
As you approach the interaction point, you could see vast looms of wiring
containing all the detection mechanisms which had been revealed.
We were able to get closer than I ever imagined we would.
In fact, it was a new experience for Mikihiko too.
Actually, I'm not working in this area usually, so this is a first time for me to be here.
We are in front of our Belle II detector and what we are seeing is that the end-cap part is opened
and the end-cap detectors are taken out so that we can see the internal detectors,
and inside there are like 40,000 wires.
It's very often that people make the misconnection and they swap the cable in some places.
If you are lucky, we can swap the cable on the other side too and everything is fine.
So, we're standing right in front of the heart of the Belle II detector.
There will be the silicon vertex detector installed in the very middle,
and then these two final focusing magnets will be inserted from the two sides,
and that's where the electrons and the positrons will come and meet at the interaction point.
But before collisions can occur, first the researchers at KEK need to generate and accelerate
the particles that come out of this tube, and to do that, you need another vast piece of equipment,
what particle physicists call 'the machine'.
This is the accelerator – SuperKEKB.
Michiru Nishiwaki took me on a tour of the tunnel that houses the beam lines.
So, we are here, and then Belle II is there.
This is the SuperKEKB accelerator.
Electrons come from there to there, and positrons come from there to there.
So, we have two rings like this.
Each ring carries either electrons or positrons – matter or antimatter.
They are accelerated to close to the speed of light using powerful radio frequency waves
and steered with a series of magnets placed all along the beam line.
The list of equipment involved in creating, accelerating, shaping and maintaining the beam is mind-boggling.
Injection beam.
A large cavity.
Dipole.
This is an accelerating cavity.
Quadrupole.
Sextupole.
Two beam pipes.
This one is for injected beam.
This one is a rotating beam.
Wave guide.
That pipe, that is also a wave guide.
Steering magnet.
This is a cryo system and this is a cooling tower.
We have four cryo systems in this building.
And then we reached this point – the positron injection line.
This is literally an antimatter injector.
So, you can see the injection line, the green magnets.
So, the positrons come from there, then go through there.
Michiru's job is to get consistent bunches of electrons and positrons travelling in opposite directions.
When the bunches reach optimum conditions, they are diverted through to Belle II and they smash together.
SuperKEKB does this much more efficiently than its predecessor,
so that Belle II will collect B mesons at a rate 40 times higher than Belle did.
Mikihiko and his team will have a lot of data on their hands.
In recent years, major experiments in particle physics have not found any direct evidence of new particles,
so many researchers now see B physics experiments as the most promising place to look for new physics,
and Belle II could play a major role in this new era.
For decades, Japan has been a world leader in big physics.
Japanese detectors join other facilities around the world,
and their vital contributions to these complex and ambitious projects is undeniable.
But when you are here, it is the scale of the experiments that really stands out –
a scale which is perhaps only rivalled by the scale of the questions they are trying to answer.